The proposed research is concerned with the effect of brain damage on semantic knowledge. Recent work in lexical comprehension has lead to the hypothesis that the aphasic's word finding problems may be causally linked to disruptions in underlying semantic representations. A series of experiments are proposed to test this hypothesis. All of them use words that are representative of a pervasive linguistic fact; namely, that a word can have many meanings. What is being assessed is the aphasic's ability to understand the multiple meanings that a word can express and the relationship that these meanings have to other concepts in their lexicon. It is expected that the tasks will reveal subtle disturbances in the mental lexicon of anterior aphasics that go undetected in semantic categorization tasks. The more serious disruptions predicted for posterior asphasics may reflect an underlying inability to use lexical knowledge in a productive way. A secondary issue concerns the difficulty that aphasics have in producing words that belong to specific grammatical categories. The stimulus materials that will be used provide a way of looking at syntactic variations within the same word. To the extent that word finding problems are form class specific, the part of speech a meaning represents should influence the aphasic's ability to understand it.